Yes, because it's illegal. If you're going to be the biggest host you're a bigger target which means you need to be more careful. What's good about the fediverse is that you have distributed instances so smaller ones can support things like piracy, and if a small one gets taken down there will be others in its place. The same game of whack a mole is what has allowed torrent tracker sites to exist. If there was one centralized torrent tracker site it would get shut down.
What the post says is exactly right. You'd be an idiot to have one account for your normal usage and piracy usage. In your normal usage you'll inevitably leak personally identifiable information. Having multiple accounts and multiple instances is the exactly right thing to do to keep piracy alive.
They're not just talking about piracy, they're linking to it. There's piracy subs on Reddit too and they're allowed because they are very careful to only talk about it and not link to it, and they're severely gimped because of that. What's great about lemmy is that instances that are on with the risk can do so without having to follow anyone else's rules and users can access it by simply having another account.